86 research outputs found
Light-waveform control of molecular processes
The control of chemical reactions is of great interest from both a fundamental and an industrial perspective. Among the many different ways to control the outcome of chemical reactions, control with the electric field waveform of laser pulses offers the possibility to control dynamics on the femtosecond, or even attosecond, timescale. This thesis presents work on a recently developed approach to control molecular processes by guiding electron motion inside molecules with the waveform of light.
The work presented in this thesis started right after the pioneering experiment on laser-induced electron localization in the dissociative ionization of molecular hydrogen with phase-stabilized few-cycle laser pulses. First, electron localization was studied for the different isotopomers H_2, HD, and D_2. The laser waveform driven strongly coupled electron and nuclear dynamics was investigated with single and two-color control schemes using near-infrared pulses as the fundamental. Furthermore, the subcycle control of charge-directed reactivity in D_2 at mid-infrared wavelengths (2.1 micrometers) was both observed experimentally and investigated quantum-dynamically. Two reaction pathways could be detected and controlled simultaneously for the first time.
Extending the approach from the prototype hydrogen molecules, which contain only a single remaining electron after initial ionization, towards complex multielectron systems was a major goal of this thesis and first achieved for carbon monoxide. Experimental and theoretical results (by our collaborators from the de Vivie-Riedle group) on the waveform control of the directional emission of C^+ and O^+ fragments from the dissociative ionization of CO shed light on the complex mechanisms responsible for the waveform control in multielectron systems. In particular, it was found that not only the dissociation dynamics but also the ionization can lead to an observable asymmetry in the directional ion emission. In CO the contributions from these two processes could not be experimentally distinguished. Studies on another heteronuclear target, DCl, showed that for this molecule mainly the ionization step is responsible for an asymmetry in the fragment emission that can be controlled with the laser waveform. Another result of the studies on complex molecules was that the angular distributions of emitted ions from the breakup of the molecules in few-cycle laser fields showed the contributions of various orbitals in the ionization step. These results were supported by a new theoretical treatment by our collaborators from the de Vivie-Riedle group based on electronic structure theory for diatomic and larger systems, where multi-orbital contributions could be taken into account. Studies of the angle-dependent ionization of both homonuclear N_2, O_2 and heteronuclear CO and DCl molecules in few-cycle laser fields clearly show the importance of multi-orbital contributions (two HOMOs or HOMO+HOMO-1).
Finally, waveform-controlled laser fields have been applied to orient molecules. Our findings on DCl suggested that samples of oriented molecular ions can be generated under field-free conditions, where the angle-dependent preferential ionization with a near single-cycle pulse is responsible for the orientation. The control of rotational wave packet dynamics by two-color laser fields was observed for CO and can be interpreted in the framework of two mechanisms: A) the hyperpolarizability orientation mechanism that dominates at low intensities, where the ionization probability is quite low and B) the ionization depletion mechanisms that prevails at high intensities, where substantial ionization occurs
ACTUAL GEOINFORMATIONAL SYSTEMS ANALYSIS FOR SOLVING AIRNAVIGATION PROBLEMS
Abstract. In this article modern achievements of the Geoinformatics for the aviation data maintenancehave been analyzed. The survey of widespread Geoinformational Systems that are used by the modernairnavigation has been described. As a conclusion the main problem for common GIS software creation hasbeen formulated.Keywords: aeronautical system, database, digital map, Geoinformational System, GIS technologies,information visualization
Моделювання зіткнення літаків з використанням методики істотних вибірок
We introduce the model of movement of two conflicting aircrafts and state the problem, we apply the importance sampling technique and elaborate an algorithm of collision modeling based on normal distributions, a small simulation studyРассмотрена модель движения двух конфликтующих самолетов. Предложены методика важных выборок и алгоритм моделирования столкновения самолетов, основанный на нормальном распределенииРозглянуто модель руху двох конфліктуючих літаків. Запропоновано методику істотних вибірок і алгоритм моделювання зіткнення літаків, заснований на нормальному розподіл
Attosecond control of electron dynamics in carbon monoxide
Laser pulses with stable electric field waveforms establish the opportunity
to achieve coherent control on attosecond timescales. We present experimental
and theoretical results on the steering of electronic motion in a
multi-electron system. A very high degree of light-waveform control over the
directional emission of C+ and O+ fragments from the dissociative ionization of
CO was observed. Ab initio based model calculations reveal contributions to the
control related to the ionization and laser-induced population transfer between
excited electronic states of CO+ during dissociation
Waveform control of orientation-dependent ionization of DCl in few-cycle laser fields
Strong few-cycle light fields with stable electric field waveforms allow controlling electrons on time scales down to the attosecond domain. We have studied the dissociative ionization of randomly oriented DCl in 5 fs light fields at 720 nm in the tunneling regime. Momentum distributions of D+ and Cl+ fragments were recorded via velocity-map imaging. A waveformdependent anti-correlated directional emission of D+ and Cl+ fragments is observed. Comparison of our results with calculations indicates that tailoring of the light field via the carrier envelope phase permits the control over the orientation of DCl+ and in turn the directional emission of charged fragments upon the breakup of the molecular ion
Field-free orientation of CO molecules by femtosecond two-color laser fields
We report the first experimental observation of non-adiabatic field-free
orientation of a heteronuclear diatomic molecule (CO) induced by an intense
two-color (800 and 400 nm) femtosecond laser field. We monitor orientation by
measuring fragment ion angular distributions after Coulomb explosion with an
800 nm pulse. The orientation of the molecules is controlled by the relative
phase of the two-color field. The results are compared to quantum mechanical
rigid rotor calculations. The demonstrated method can be applied to study
molecular frame dynamics under field-free conditions in conjunction with a
variety of spectroscopy methods, such as high-harmonic generation, electron
diffraction and molecular frame photoemission
Wavelength dependence of electron localization in the laser-driven dissociation of H
We theoretically investigate the laser wavelength dependence of asymmetric
dissociation of H. It is found that the electron localization in
molecular dissociation is significantly manipulated by varying the wavelength
of the driving field. Through creating a strong nuclear vibration in the
laser-molecular interaction, our simulations demonstrate that the few-cycle
mid-infrared pulse can effectively localize the electron at one of the
dissociating nuclei with weak ionization. Moreover, we show that the observed
phase-shift of the dissociation asymmetry is attributed to the different
population transfers by the remaining fields after the internuclear distances
reach the one-photon coupling point.Comment: 11 pages, 7 figure
SISTEM MONITORING MENGGUNAKAN KAMERA IP
RIFKI YUSUF SETIAWAN, 2010, SYSTEM MONITORING USING IP
CAMERA. 3rd Diploma Program Computer Science, Faculty of Mathematics and
Natural Science, Sebelas Maret University of Surakarta.
The level of criminality was quite high, pushed the existence of the
production of the monitoring system which gave the more effective safety.The
main aim of this final report is to investigate the way of designing and developing
program to monitor a room by using IP camera.
The data were collected though experiment, observation, and library
research. This study revealed that IP Camera was capable of monitoring room
automatically and the software to manage the displayed was created by delphi 7 .
Based on the findings, it could be concluded that we could monitor a
room with IP camera.
Keyword : IP camera, security, delphi 7, monitorin
Searching for pathways involving dressed states in optimal control theory
Selective population of dressed states has been proposed as an alternative control
pathway in molecular reaction dynamics [Wollenhaupt et al., J. Photochem.
Photobiol. A: Chem., 2006, 180, 248]. In this article we investigate if, and under
which conditions, this strong field pathway is included in the search space of
optimal control theory. For our calculations we used the proposed example of the
potassium dimer, in which the different target states can be reached via dressed
states by resonant transition. Especially, we investigate whether the optimization
algorithm is able to find the route involving the dressed states although the target
state lies out of resonance in the bare state picture
Attosecond electron spectroscopy using a novel interferometric pump-probe technique
We present an interferometric pump-probe technique for the characterization
of attosecond electron wave packets (WPs) that uses a free WP as a reference to
measure a bound WP. We demonstrate our method by exciting helium atoms using an
attosecond pulse with a bandwidth centered near the ionization threshold, thus
creating both a bound and a free WP simultaneously. After a variable delay, the
bound WP is ionized by a few-cycle infrared laser precisely synchronized to the
original attosecond pulse. By measuring the delay-dependent photoelectron
spectrum we obtain an interferogram that contains both quantum beats as well as
multi-path interference. Analysis of the interferogram allows us to determine
the bound WP components with a spectral resolution much better than the inverse
of the attosecond pulse duration.Comment: 5 pages, 4 figure
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